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Sunday, June 12, 2011

Porsche Publicly Debuts its Electric Boxster E, But It’s Not For Sale

We previously reported that Porsche was working to develop three electric Boxster prototypes, and last week three Boxster Es made their public debut at the Michelin Challenge Bibendum in Berlin. Of Porsche’s three electric test Boxsters, one sports all-wheel drive in the form of an electric motor on the front and rear axle while the other two are rear-wheel drive. Porsche claims the dual-motor Boxster E delivers Boxster S levels of driving dynamics, including a 5.5-second 0-to-62 run on the way to a top speed limited (would that be electronically?) to 124 mph. The combined output of the two motors is 241 hp and 398 lb-ft of torque, fed through a single-speed transmission. The two single-motor Boxster Es are a bit less impressive, creeping from 0 to 62 mph in 9.8 seconds and topping out at 93 mph. Dropping the front motor halves the rear-wheel-drive Boxster E’s power output, to just 120 hp and 199 lb-ft of torque.

In the AWD E, the front motor is mounted where the fuel tank resides in a conventional Boxster, and the rear motor and battery pack are mounted where the mid-engine roadster’s flat six normally lives. The battery has been cleverly attached to the engine mounts, ensuring crash-safety characteristics that are almost identical to a gas Boxster’s. Porsche notes that the battery shares the same “drop-out” capabilities as the conventional Boxster’s engine, which is removed from the underside of the car. This would theoretically allow for quick battery swaps. The water-cooled battery pack is comprised of 440 individual lithium-iron-phosphate cells that, combined, store 29 kWh of energy—26 kWh of which is accessible. Porsche claims a range of 107 miles per nine-hour charge. An electronic control unit manages the power distribution between the front and rear axles. The single-motor E shares its rear motor and battery layout with the dual-motor E, minus the front motor.

The electric Boxsters maintain their rear trunk capacity, and the front capacity is only slightly reduced by a charging socket and its hardware. The E’s instrument cluster loses its tachometer, which is replaced by an E-Power meter that shows how much power is being used by the motor and how much is being generated by the regenerative braking system. The Boxster E allows drivers to select among a range of braking regen levels, which Porsche refers to as a kind of “on-demand” engine-braking (motor-braking?) effect. Think of it as downshifting. The instrument pod to the right of the E-Power meter displays range info and the effects of various electricity-sapping accessories on the car’s range.

While the electric Boxster is compelling, the chances of it making its way into production are virtually nil—so we were told by Porsche reps on a recent trip to sample the new Panamera Hybrid. The Boxster Es, then, exist as battery test beds from which Porsche can cull knowledge to apply to its quickly expanding hybrid lineup. Take, for example, the Panamera Hybrid: it has a small nickel-metal hydride battery that weighs 154 pounds and has a 1.7-kWh capacity. The Boxster E’s lithium pack weighs 388 percent more—751 pounds versus 154 pounds—but packs 1606 percent more capacity. Using some fuzzy math, that means that if the Panamera hybrid’s 1.7-kWh battery pack was of the lithium variety, its weight could be reduced to just 44 pounds. While that is an estimate of the roughest kind, a savings of approximately 100 pounds seems to us like a good enough reason to explore battery tech.

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